A ladder is disclosed in U.S. Pat. No. 4,199,040, of the same inventor and assignee as this invention, which comprises a single stringer or central tread support disposed between upper and lower levels at a predetermined angle of inclination and having an array of half treads on each side of the stringer, each array being vertically spaced from the other along the length of the stringer. The half treads are affixed to and laterally extend from the respective sides of the stringer, and each includes an integral outwardly extending portion which terminates in a plane which is forward of a plane passing through the front edges of the treads. First and second handrails are disposed in this forward plane and are affixed to and supported by the outwardly extending tread portions. This novel ladder can be disposed at a relatively steep angle in comparison to a conventional ladder of the same tread width and riser height and provides sufficient safety and comfort to permit balanced use of the ladder, even without holding onto the handrails.
Ladders are known in which treads or rungs are alternately arranged along a single stringer or pole, as shown in U.S. Pat. Nos. 4,061,202 and 4,069,892. In ascending and descending ladders of this known type, a user must face the ladder and support himself by holding onto the rungs to guide his ascent or descent. Such ladders cannot be descended facing forwardly, as with a stairway, and these ladders require a fair degree of dexterity on the part of a user and are not very comfortable to use, and are sometimes unsafe.
In most stairways, the treads extend uniformly across the width of the stairway, each tread being of the same front-to-back dimension. The treads are supported by one or more stringers. Examples are shown in U.S. Pat. Nos. 3,310,132 and 3,467,220. Stairways are shown in U.S. Pat. Nos. 858,199 and 4,125,175 in which the treads are set back on alternate half portions to provide foot clearance in moving from the non-set-back portion of a tread to the next non-set-back portion of a succeeding tread, for the purpose of facilitating use of the stairway which is inclined at a relatively steep angle of inclination. In the structure of U.S. Pat. No. 858,199, each tread has a set-back portion and a non-set-back portion and is disposed between and supported by a pair of side stringers. In the structure of U.S. Pat. No. 4,125,175, the treads are similarly constructed and are each connected to an adjacent tread by a pair of vertical supports. Neither of these disclosed stairways employs any handrails.